Discharge lamp starting circuit



June 13, 1944- G. A. FREEMAN 2,351,499

DISCHARGE LAMP STARTING CIRCUIT Filed Sept. 27, 1941 INVENTOR ATTORNEY Patented June 13, 1944 'JUNITED STATES P NT" OF DISCHARGE LAMP STARTING CIRCUIT George A, Freeman, East Orange, N. J., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa

of Pennsylvania I a corporation Application September 27,1941, Serial No. 412,578

4Claims.

creases; and as the operating or lamp voltage approaches line voltage, the problem of starting and operating becomes more and more complex.

Although many differenttypesof circuits have likewise been employed in connection with discharge lamps wherein the operating voltage very closely approaches line voltage, they have not been very satisfactory. This is primarily due to the application of the higherstarting voltage to the thermionic electrodes of the lamp. before they have been heated to maximum electron-emitting temperature, causing sputtering of the electrode coating, resulting in comparatively short lamp life. 1

It is accordingly an object of the present invention to provide a starting and operating circuit for a discharge lamp requiring a lamp voltage closely approaching line voltage.

Another object of the present invention is the provision of a starting and operating circuit for a discharge lamp requiring a lamp voltage approaching available line voltage and wherein the higher starting voltage is not applied to the lamp until the thermionic electrodes have been heated to maximum electron emissivity.

A further object of the present invention is the provision of a starting and operating circuit for a discharge lamp wherein the higher starting voltage is not applied to the thermionic electrodes of the lamp until they have been heated to maximum electron emissivity, thus prolonging the useful life of the lamp.

Still further objects of the present invention will become obvious to those skilled in the art by reference to the accompanying drawing, where- .in the single figure is a diagrammatical illustration of the starting and operating circuit for a discharge lamp in accordance with the present invention.

Referring now to the drawing in detail, a discharge lamp 5 is shown provided with the customary thermionic electrodes 6 and I comprising filaments coated with a material which gives maturely.

off a copious flow -of electrons when heated, such .as an oxide of barium, strontium, or the like.

The lamp envelope is-provided with a gas, such as argon, neon, helium or the like, to facilitate starting, and a small quantity of a vaporizable metal, such as mercury. The interior of the envelope is also coatedwith a material which is excited by the invisiblev ultra-violet radiations to produce visible light.

As shown, the lamp isdesigned to operate from the customary domestic source of electrical energy of approximately 110 volts which supplies the energy for firstheating the electrodes to an electron-emitting .temperature and thereafter supplies the discharge current... Assuming, for example, the lamp is of about 40-watt consumption, the electrodes will have such a spacing that approximately volts is required to sustain a discharge, which very closely approaches the line voltage of volts. Moreover, a lamp of this wattage requires astarting voltage surge in'excess of 220 volts once the electrodes ,are heated to maximum electron-emitting temperature.

. ,For the purpose of heating the electrodes 6 and I to an electron-emitting. temperature, one terminal of the electrode. 6 is connectedto one side of the domestic source of supply, and in a similar manner one terminal of the electrode! isconnected through a reactor or choke coil 8, capacitor'fl, and switch' I 0', to the opposite side of the source of supply of '110 volts. To complete a series circuit to the electrodes, their remaining terminals are preferably connected together through an inductance l2 as shown in the drawing. The circuit thus far described differs not at all from the prior art since it is substantially at resonance, and includes elements, previously employed. Although such circuit would operate to initiate a discharge between the electrodes 6 and ".1 upon closure of the switch Ill, there is nothing to prevent the high voltage developed across inductance l2 from starting the discharge before the electrodes have attained proper electronemitting temperature which invariably causes sputtering of the electrode coating with resulting short'lainp life.

To prevent such undesired result in accordance with the present invention,.the constants of'the circuit are so, designed thatinsuflicient current initially flows through the reactor 8 and inductarice l2 to heat the electrodes 8 and I up to a temperature where a discharge will occur pre- The net reactance ofcapacitor S'plus reactor 8 must be capacitiveand'of such value to fix the arc current at its rated value which is .45 ampere for a 40-watt lamp. The net reactance of the capacitor 9 plus the reactor 8 and inductance I2 is reactive and of such value as to develop ape proximately 220 volts across thei'nductance i2 for operating a glow switch This voltage across inductance lI-is insufllcien't to initiates" discharge between the electrodes 6' and' l,"particularly as they are not heated'due "tothe now 01' insufllcient current therethrough. The-circuit also has a leading power i'actor'oi over 80%.

To complete a series heating"circuitfof'the filamentary electrodes to assure heated to maximum electron-'emittingtemperm ture and at the same time initiate a-discliarge once they are heated, the glow relay tube II- above mentioned is provided for short-circuiting the inductance II. This glow relay tube-ll is of the type shown and described in Patent-No. 2,200,443, issued May 14, 1940, to-E. C. Dench, and assigned to the same assignee as the present invention, and it is believedthat-it-need not'be' herein described in detail. It should'sufllce to say that upon the application of the voltage for which it is designed, which in the present instance is 220 vo1ts,a glow discharge occurs whichwould not occur at the line voltage, since the-glow relay tube is inoperative at 110' volts. This-glow discharge heats the electrodes of the relay tube V and since one is a bimetallic electrode, itdefiects into engagement with the other" electrode to short-circuit the discharge;

Inasmuch as the glow relay tube, as hereinbefore mentioned, is in parallel with the'inductance l2 and upon closure of the switch 10' avolt age of approximately 220 volts is induced across the inductance l2, such voltage is sumcient t'o initiate the discharge in the glow relay tube 13.-

Also, upon engagement of the electrodes of the ing temperature very rapidly, the time delay' vduring which the electrodes of the glowrelay tube remain in engagement with each other being suflicient for this purpose.

When the bimetallic electrode cools and separates from its cooperating electrode,- a high voltage surge results from the series reactor 8 sufficiently above 220 volts to initiate a positive column discharge between the now preheated lamp electrodes 6 and I. Once this latter discharge starts, the lamp voltage drops to approximately 100 volts which is insufilcient to again start a discharge in the glow relay tube. Moreover, the filamentary electrodes 6 and 1 are then heated mainly by the discharge since circuit flow through the inductance I2 is reduced. If, however, the lam-p 5 should for any reason fail to start on the first operation of the glow relay tube l3, the latter will again repeat its cycle of operation without deleterious effect upon the lamp electrodes until the lamp doesstart.

It should perhaps be pointed out that although a glow relay tube |3* will operate satisfactorily in the circuit arrangement such as shown in the above mentioned patent,this is because the lamp therein shown is of shorter length wherein the considerably below line voltage. However, wit

longer lamps'which have voltages approaching more closely the line voltage, a higher voltage glow relay tube is used so that the lamp voltage or line voltage, which are of the same order oi magnitude, will not operate it.

For example, it the relay is designed for a line voltageoi volts, as in the above noted patent, lt'would continue to repeat its operation when employed with a higher voltage lamp which has a lampvoltage approximating that of line voltage and the lamp would not start. To avoid this by employing a relay tube designed for 220- rent'ilowior'heating the electrodes oi the lamp and at the same time the circuit would be subject to the disadvantage avoided by the present invention, asjbefore mentioned, of allowing application oi', a highstartlng voltage prior to the electrodes being heated to optimum electronemitting temperature.

In the preferred form thus'i'ar described it will be obvious that there is a small flow of current through the electrodes prior to operation of the glow relay tube, which as before mentioned is insui'licient to heat the lamp electrodes to any appreciable extent. By the same token, during operation ot'th lamp there will likewise be a flow of the samelow current value through the lamp electrodesand through the inductance l2 since the latter completes a series heating circuit when not short-circuited by the glow relay tube.

Although it is believed preferable to allow this small flowv of current through the electrodes, it may be avoided if desired by connecting the inductance ln the circuit as shown at ll by the'dotted lines in "the 'flgure, in lieu of the parallel connection with the glow relay tube I! on the opposite side of the lamp electrodes, as shown by the solid lines for the inductance 12. This arrangement still permits the voltage built up across the inductance H to be impressed across a glow relay II with resultant operation .of the latter and at the's'ame time prohibits any flow of heating current through the lamp electrodes prior to operationof the glow relay tube, as well as during operation of the lamp. The total efllciency of the circuit is accordingly enhanced somewhat since the current through the inductance I4 would not flow through the lamp electrodes where heat loss results therefrom.

It should perhaps be noted that while the preferred circuit arrangement as above described is designed primarily for the starting of a discharge lamp from a commercial source of supply of 110 volts and where the lamp voltage closely approaches line voltage, such arrangement also will operate efficiently when employed with a line voltage of 220 volts and where th lamp is designed for operation from such source of supply, but where the lamp voltage is below line voltage, obviously the constants of'the circuit would be somewhat different with this line voltage of 220 volts. This particular circuit arrangement when employed with a line voltage of 220 volts compensates for line voltage fluctuations in holding the electrodes at optimum emitting temperature.

For example, assuming the line voltage is 220 volts instead of 110 and that the operating voltage oi. lamp 5 is substantially below this voltage, during operation of the lamp as the line voltage decreases due to fluctuations, more current-will flow through the inductance I2 and lesscurrent will flow through the lamp. The lower heating of the cathode from the arc is compensated by increased heating resulting from increased current flow through the inductance l2. ,Light output from. the lamp is lowered considerably at the same time due to reducedarc current. A further advantage of this circuit when employed on a 220- volt line resides in the fact that it can be employed in applications where a variable light intensity is desired without deleterious eifect on lamp life.

It thus becomes obvious to those skilled in the art that a circuit for a-discharge lamp isherein provided in which the lamp is eill'ciently operable from the customary domestic source of potential despite the fact that its operating voltagevery closely approaches line voltage. Furthermore, the

constants'of the circuit are so designed that relatively low current flows through the filamentary electrodesuntil the circuit is conditioned to enable them to be heated to optimum electron-emitting temperature prior to the application of the high starting voltage, thus preventing sputtering of the electron-emitting elecrode coating and prolonging the useful life of the lamp. Moreover, by connecting the inductance on the opposite side of the lamp electrodes to the glow relay tube, flow of any current through the lamp electrodes prior to operation of the glow relay can be readily prevented. By employing the circuit arrangement of the present invention in connection with a 220- volt source and wher the lamp voltage is materially lower than line voltage, a variable light source is obtained and wherein line voltage fluctuations arecompensated'for by automatically increasing the flow of current through the inductance as the line voltage decreases, thus preventing temperature prior to the initiation of a discharge therebetween, a source of electrical energy of the customary domestic potential for preheating said electrodes and for thereafter sustaining a positive column discharge therebetween, a reactor and a capacitor'interposed between said source and one of the electrodes of said lamp to render the operating circuit for said lamp capacitive, aninductance interconnecting the electrodes of said lamp to complete a reactive starting circuit to said source and adapted to initially have a voltage impressed thereacross which is approximately doublethat of said domestic source but insufficient to initiate a discharge in said lamp, and means in electrical parallel with said inductance and automatically operable to short-circuit the latter and cause the electrodes of said lamp to be heated to optimum electron-emitting temperature from said source and for thereafter removing the short-circuit condition of said inductance with attendant causation of a high voltage surge from said reactor and capacitor sufliciently above the voltage across said inductance to initiate a discharge between said preheated electrodes.

2. A starting and operating circuit for a discharge lamp comprising a discharge lamp operable at a voltage approaching normal line voltage and provided with filamentary electrodes adapted to be heated to an electron-emitting temperature prior to the initiation of a discharge therebetween, a source of electrical energy of the customary domestic potential for preheating said electrodes andfor thereafter sustaining a positive column discharge therebetween, a reactor and a capacitor interposed between said source and one of the electrodes of said lamp to render the operating circuit for said lamp capacitive, an inductance interconnecting the electrodes of said lamp to complete a reactive starting circuit to said source and adapted to initiallyhave a voltage developed thereacross which is approximately double that of said domestic.

source but'insufflcient to initiate a discharge in said lamp, the constants of said circuit being such that insufficient current initially flows through the electrodes of said lamp to heat the same during the imposition of a voltage higher than line voltage across said inductance, and means in electrical parallel with said inductance andautomatically operable to short-circuit the latter and cause the electrodes'of said lamp to be heated to optimum electron-emitting temperature from said source and for thereafter removing the short-circuit condition of said inductance with attendant causation of a high voltage surge from said reactor and capacitor sufficiently above the voltage across said inductance to initiate a discharge between said preheated electrodes. i

3. A starting and operating circuit for a discharge lamp comprising a discharge lamp operable at a voltage approaching normal line volt-v age and provided with filamentary electrodes adapted to be heated to an electron-emitting temperature prior to the initiation of a discharge therebetween, a source of electrical energy of the customary domestic potential for preheating said electrodes and for thereafter sustaining a positive column discharge therebetween, a reactor and a capacitor interposed between said source and one of the electrodes of said lamp to render the operating circuit for said lampv capacitive, an inductance interconnecting the electrodes of said lamp to complete a reactive starting circuit to said source and adapted to initially have a voltage impressed thereacross which is approximately double that of said domestic source but insuificient to initiate a discharge in said lamp, and a glow relay tube in electrical parallel relation with said inductance and automatically operable to shortcir'cuit the latter and cause the electrodes of said lamp to be heated to optimum electron-emitting temperature from said source and for thereafter removing the short-circuit condition of said inductance with'attendant causation of a high voltage surge from said reactor and capacitor sufiicientlyabove the voltage across said inductance to initiate a discharge between said preheated electrodes.

4. A starting and operating circuit for a discharge lamp comprising a discharge lamp operable at a voltage approaching normal line voltage and provided with filamentary electrodes adapted to be heated to an electron-emitting temperature prior to the initiation of a discharge therebetween, a. source of electrical energy oi the customary domestic potential for preheating said electrodes and for thereafter sustaining a positive column discharge therebetween, va. reactor and acapacitor interposed between said source and one of the electrodes of said lamp to render the operating circuit for said lampcapacitive, an inductanceinterconnecting the electrodes of said lamp to complete a reactive starting circuit to said source and adapted to initially have a voltage induced thereacross which is approximately double that of said domestic source but insuflicient to initiate a discharge in said lamp, the constants of said circuit being such that insufficient current initially flows through perature from said ourc ei and for thereafter removing the short-circult condition of saidinductance withv attendant causation ot a high voltage surge from said reactor and capacitor sufilciently above the voltage across said inductance to initiate adischarge betweensaid preheated electrodes. GEORGE A. FREEMAN. 

